Communication devices, such as mobile telephones, tablets, computers or the like, may perform wireless communication with a remote node in order to exchange information therewith. Early communication systems operated in a time multiplexed manner such that if a transmitter device was on, then its receiver was off. This approach simplified transmitter and receiver design but was an inefficient use of bandwidth and/or data throughput. The desire to use bandwidth more efficiently and/or increase data throughput has resulted in radio and data communications systems moving towards duplex operation and multi-channel operation. As a result, for a transmitter and receiver pair, commonly referred to as a transceiver, the transmitter may be transmitting concurrently with the receiver seeking to receive a signal from a physically remote transmitter. The transmitter and the receiver may be operating concurrently at different frequencies separated by a “duplex frequency”. Such systems are known as Frequency Division Duplex (FDD) systems. Alternatively, in a full duplex system, the transmitter and receiver may operate concurrently at the same or substantially the same frequency. Under such circumstances, the signal from the transmitter of the transceiver may have a power at the receiver of the transceiver which is much greater than that of a wanted signal or wanted signals from one or more remote transceivers.
It is known that isolators and filters, optionally with the use of multiple antennas, can be used to reduce leakage from a transmitter of a transceiver to the associated receiver of the transceiver. However, these components still allow appreciable amounts of power to appear at the radio frequency (RF) front end of the receiver. This leakage can include the data being transmitted by the transmitter, and noise from the transmitter. The data is constrained into well-defined frequency bands known as channels. The noise can be wideband and can leak into channels that the receiver is seeking to recover data from. Wide band noise from the transmitter power amplifier can degrade the receiver's sensitivity. Wideband transmitter noise can also leak into the receiver in frequency division duplex systems.
Even in systems where the transmitter should notionally be “off” whilst a receiver is “on”, “off” may mean in a quiescent state rather than fully depowered and hence residual noise may still leak from the transmitter to the receiver.